Heretofore, a technique of this type is known as a flow rate controller disclosed in JP 2007-206936A. This flow rate controller includes a proportional electromagnetic valve arranged to proportionally control the flow rate of a fluid, a flow rate sensor for detecting the flow rate of the fluid, and a control circuit for controlling the proportional electromagnetic valve so that a detection value of the flow rate sensor reaches a predetermined target flow rate.
Herein, the proportional electromagnetic valve disclosed in JP 2007-206936A includes a coil wound on a bobbin, a fixed core and a movable core both mounted in the hollow of the bobbin, a valve element provided at one end of the movable core, and a spring that urges the movable core and the valve element in a valve closing direction. The proportional electromagnetic valve further includes a valve chamber, a lead-in path for leading a fluid into the valve chamber, a valve seat formed in the valve chamber, and a lead-out path for leading the fluid out of the valve chamber through the valve seat. During non-energization of the coil, this proportional electromagnetic valve presses the movable core by an urging force of the spring to bring the valve element into contact with the valve seat for valve closing. On the other hand, during energization of the coil, the coil is excited, causing the fixed core to attract the movable core against the urging force of the spring, thus separating the valve element from the valve seat for valve opening. By controlling energization of the coil, the opening degree of the valve element is adjusted to control the flow rate of the fluid.
However, in the aforementioned proportional electromagnetic valve, both the fixed core and the movable core are mounted together in the hollow of the bobbin. Accordingly, the movable core has a sliding surface in contact with the bobbin. Due to sliding resistance, the movable core does not move smoothly. Thus, abrasion powder is generated between the movable core and the bobbin, which may deteriorate the life of the proportional electromagnetic valve.
Therefore, the present applicant previously proposed a proportional electromagnetic valve arranged such that a movable core is not placed in the hollow of a bobbin so that the movable core does not slide in contact with the bobbin in moving a valve element, differently from the aforementioned proportional electromagnetic valve. This proportional electromagnetic valve of a non-sliding type is disclosed in JP 2002-357280A and JP 2003-14022A. A proportional electromagnetic valve of such type is shown in a cross sectional view in FIG. 24. The proportional electromagnetic valve 81 includes a bobbin 83 on which a coil 82 is wound, a fixed core 84 fixed in the hollow 83a of the bobbin 83, a case 85 containing the coil 82 and others, a movable core 86 placed in correspondence with a lower end of the fixed core 84 and adapted to be attracted by the fixed core 84, a valve element 87 fixed at a lower end of the movable core 86, and a plate spring 88 fixed at the lower end of the movable core 86 and in concentric relation with the valve element 87. The proportional electromagnetic valve 81 further includes a body 89, a valve chamber 90 in which the valve element 87 is placed, a valve seat 91 provided in the valve chamber 90, a lead-in path 92 for leading a fluid into the valve chamber 90, and a lead-out path 93 for leading the fluid out of the valve chamber 90 via the valve seat 91. Those valve chamber 90, valve seat 91, lead-in path 92, and lead-out path 93 are formed in the body 89 respectively. In the body 89, an orifice 94 is formed immediately downstream of the valve seat 91 between the valve seat 91 and the lead-out path 93. The plate spring 88 is made of a circular thin plate formed with cutouts each having a predetermined shape. A central portion of the plate spring 88 is fixed to the movable core 86 and in concentric relation with the valve element 87. An outer peripheral edge of the plate spring 88 is fixedly held between the body 89 and the case 85. This proportional electromagnetic valve 81 is arranged to control movement of the valve element 87 with respect to the valve seat 91 by balance between the attractive force of the fixed core 84 generated when the coil 82 is excited by energization (current supply) and the urging force of the plate spring 88.